Key Takeaways
Q195, Q235 and Q345 are ordinary structural carbon steels - not wear-resistant steels. For abrasion service, specify NM-series wear plate (e.g. per GB/T 24186) or equivalent.
Q195 and Q235 are defined in GB/T 700; Q345 is a higher-strength low-alloy grade in GB/T 1591.
Flat bar is supplied in a wide range of widths and thicknesses for structural frames, brackets, machinery parts and general fabrication.
Welding Q345 sections above about 25 mm may need preheat (commonly 80–120 °C depending on conditions) to avoid cold cracking.
1. Setting the Record Straight: Not Wear-Resistant Steel
The original title described Q195/Q235/Q345 flat bar as "wear resistant". That is incorrect. These grades are ordinary carbon structural steels used for their strength, weldability and economy - not for abrasion resistance. Where components are exposed to severe sliding or impact abrasion (buckets, liners, chutes), the correct material family is wear-resistant steel such as the NM-series (for example per GB/T 24186) or equivalent quenched-and-tempered wear plate, which is supplied on hardness and impact-wear performance. Choose the grade by the actual failure mode: structural strength, or abrasion.
2. The Grades
| Grade | Standard | Typical use |
|---|---|---|
| Q195 | GB/T 700 | Light structures, wire, small sections, general fabrication |
| Q235 | GB/T 700 | General structural steel: frames, brackets, supports, mild machinery parts |
| Q345 | GB/T 1591 | Higher-strength structural and machinery components where weight saving matters |
Yield and tensile values are thickness-dependent and set by the current standard; always confirm against the standard edition and the mill COA.
3. Flat Bar: Sizes and Supply
Hot-rolled carbon steel flat bar is supplied as rectangular-section bar in a wide range of widths and thicknesses - typical width-thickness combinations cover light strapping sections up to heavy structural flats; exact availability is confirmed per size and grade. Edges are normally as-rolled. Flat bar is cut to length, bundled and shipped for fabrication; specify grade, dimensions (width × thickness × length), quantity and any straightness requirement.
4. Fabrication and Welding Notes
All three grades weld readily with conventional processes. Q235 welds without special measures in most sections. For Q345, low carbon equivalent (typically around 0.40–0.45%, confirm per heat) permits welding with E50-class electrodes without preheat for thin sections; for thick sections (above about 25 mm) or cold-weather welding, preheating to roughly 80–120 °C is recommended to prevent cold cracking. Excessive sulfur and phosphorus impair weldability, so keep to standard limits.
5. If You Do Need Wear Resistance
For abrasion applications, ask for wear-resistant steel - for example NM360/NM400/NM450 or equivalent per GB/T 24186, or a comparable quenched-tempered wear plate to the applicable standard - and specify hardness grade and plate thickness rather than a structural carbon grade.
Frequently Asked Questions
1. Is Q345 the same as wear-resistant steel?
No. Q345 is a higher-strength structural steel (GB/T 1591). Wear-resistant grades are a separate family (NM-series per GB/T 24186 or equivalent).
2. What sizes of flat bar are available?
Widths and thicknesses span light to heavy structural sections; confirm the exact size, grade and quantity with the supplier.
3. Does Q345 need preheat before welding?
Thin sections generally do not; thick sections (above about 25 mm) or low-temperature conditions benefit from preheating around 80–120 °C.
4.Applicable Scenarios?
Building steel beams/columns, bridges, cranes, vehicle chassis, ship structures, pressure vessels, mining machinery, wind turbine towers.
5.Can it be used in low-temperature environments?
Grade C ≥ 0℃, Grade D ≥ -20℃, Grade E ≥ -40℃ can be used directly; Grades A/B are not suitable for low temperatures.
6.How is its weldability?
Excellent, low carbon equivalent (Ceq≈0.42%), suitable for manual arc welding with E50 series electrodes, no preheating required (for thin parts).
7.Is it prone to cracking during welding?
For thick parts (>25mm) or low-temperature welding, preheating to 80–120℃ is required to prevent cold cracking; excessive S/P can easily lead to hot cracking.